Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface.

All text is shown in broken lines. The broken lines showing a display screen or portion thereof, text, and portions of the graphical user interface form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 